The present invention is generally directed to systems for selectively distributing video presentations to viewers and more particularly concerned with systems for enabling viewers to interactively select still frame video images and accompanying audio to be distributed to them over a television system such as a cable network.
A still frame television distribution system of the type to which the present invention applies is disclosed, for example, in U.S. Pat. No. 4,734,764. Such a system is particularly suited for interactive video services such as home shopping, financial transactions, education and the like. Generally speaking, in this type of system a viewer sends an indication to a central location describing a video presentation which he desires to receive, e.g. houses being offered for sale by a real estate service. Video frames which show the available houses are individually retrieved from a suitable video storage medium, and each frame is encoded with an address. Other viewers can simultaneously request other presentations available on the system. All of the addressed frames selected by the various viewers are multiplexed onto a transmission medium, such as the trunk cable of a cable television system, and transmitted at the standard television frame rate, e.g. 30 frames per second under the NTSC standard, over a channel associated with the video presentation service. Frame stores are positioned at various locations along the length of the transmission medium, and each is provided with a unique address. The transmission path along which the video signals travel from the central location to the frame stores is referred to as a primary transmission path. When a video frame is encoded with the address of a particular frame store, that frame store retrieves the frame from the primary path, stores it in a memory, and then continually retransmits the stored frame at the standard television frame rate along a secondary path located between the frame store and the viewer's television receiver. In the embodiment disclosed in the '764 patent, this secondary path can comprise a distribution cable which branches from the trunk cable, and/or a drop cable which branches from the distribution cable to an individual viewer's home. The transmission of the frame along the secondary path can be on the same channel as the primary path, or a different channel. The continually transmitted frame appears as a still frame on the viewer's receiver. When the viewer desires to see the next frame in the presentation, a signal is sent to the central location over the telephone line, and this frame is retrieved, encoded with the address of the viewer's frame store, and transmitted over the primary path to be displayed in the same manner.
The system disclosed in the '764 patent provides a practical approach which enables the selective distribution of video presentations to be implemented in a conventional television system having a finite number of available channels. Unlike other distribution systems which rely upon dedicated transmission paths or transmission channels for individual subscribers, a system as disclosed in the '764 patent requires as little as one channel on the television system to provide selective distribution to all viewers. If the television system has sufficient capacity, it is possible to employ a first channel or limited number of channels for transmission over the primary path, and a different channel common to all viewers for transmission over the secondary paths.
It is desirable to build upon the fundamental principles disclosed in the '764 patent in a manner which increases the functionality, and hence the effectiveness, of such a system. For example, it is desirable to increase the capacity of the system in a manner which increases the efficiency with which transmission network resources are utilized. It is also desirable to reduce the likelihood that viewer contention problems could arise as the number of viewers having access to the system increases.
Accordingly, it is a general objective of the present invention to provide a novel distribution system which utilizes the capacity of a television system, particularly a cable system, in an economic fashion, and thereby minimizes contention problems as the number of viewers in the system increases. Along these lines, it is a more specific objective of the present invention to provide a distribution system which allows the expansion of services in an economic fashion and provides the viewer with greater and easier access to the available video presentations, while at the same time ensuring the privacy of presentations selected by the viewer. To this end, it is an objective of the invention to provide a novel distribution system in which various types of presentations can be specifically directed to certain viewers. It is a further objective to provide a distribution system that is easy to install at the viewer location.